This application claims the benefit of Korean Application No. 2000-86260, filed Dec. 29, 2000, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to phosphors for use in a display device such as a vacuum fluorescent display (VFD) or field emission display (FED).
2. Description of the Related Art
Like cathode ray tubes (CRTs), VFDs are self-radiating displays that use phosphors. VFDs are widely used in applications such as digital displays of household electric appliances and gauge panels of automobiles. VFDs have mainly been used for low-capacity, small-sized products to simply display numbers, characters, and signs. However, VFDs are currently in use for high-density graphic image displays. In the near future, a full color VFD having a large display capacity will become commercially viable.
FEDs have received considerable attention as a next generation display device having the advantages of flat panel displays such as liquid crystal displays (LCDs) and CRTs. Thus, much research on FEDs continues to be actively conducted. FEDs, which operate on the principle of field emission of electrons from microscopic tips, are known to be capable of overcoming the drawbacks of CRTs, such as excessive bulk and weight, and the drawbacks of LCDs, such as high manufacturing cost and limited site and viewing angle. Furthermore, since FEDs have various advantages such as a thin film form, low power consumption, low manufacturing cost, excellent temperature characteristics, and high-speed operation, they can be used in a wide variety of applications ranging from home televisions to industrial equipment and computers. In particular, FEDs are likely to be widely used in commercial applications such as notebook PCs, monitors, and televisions, like thin film transistor (TFT) LCDs.
A phosphor able to be excited by a low-velocity electron beam is required to be used in VFDs or FEDs in order to emit light at an anode operating voltage no greater than 1 kV. Conventional phosphors that are excitable by low-velocity electron beams are divided into two types by the resistance of a host lattice: one is a phosphor based upon a low-resistance host matrix, and the other is a phosphor based upon a high-resistance host matrix and having a phosphor layer formed by adding a conductive material to reduce the resistance of the host matrix.
The host matrix of the latter high-resistance phosphors mostly contain sulfur (S), and thus the sulfur-containing phosphor is referred to as a xe2x80x9csulfide phosphor.xe2x80x9d It is known that the sulfide phosphor is readily decomposed when bombarded by electrons, and the decomposed sulfide phosphor is scattered within a VFD. The sulfide-based material impinges on a cathode in the VFD, thereby contaminating the cathode and thus degrading the emission power of the VFD. Another problem with the sulfide phosphor is that the sulfide impinges on other oxide phosphors to contaminate an anode. Additionally, a ZnCdS-based host matrix contains a pollutant such as cadmium (Cd), which adversely affects the environment.
To overcome the drawbacks of conventional phosphors, a phosphor prepared by adding a rare earth element and a Group III element to a host matrix composed of alkali earth metal oxide and titanium (Ti) oxide is disclosed in Japanese Patent Laid-open Publication No. Heisei 8-85788 and U.S. Pat. No. 5,619,098, the disclosures of which are incorporated by reference. The phosphor host matrix does not contain sulfur or cadmium (Cd) and is excited by low-velocity electron beams to emit light. However, this phosphor has not yet been put into practice due to its having a short lifespan.
To solve the above and other problems, it is an object of the present invention to provide a phosphor whose host matrix does not contain sulfur and which has a long lifespan and improved luminance and does not contain cadmium.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
Accordingly, to achieve the above and other objects, a phosphor according to an embodiment of the present invention complies with formula (1) below, has a perovskite structure and contains samarium (Sm):
MTiO3: (A, B)xe2x80x83xe2x80x83(1)
where M is an alkali earth metal, A is an element selected from the group consisting of cerium (Ce), praseodymium (Pr), europium (Eu), terbium (Tb), and thulium (Tm), and B is a Group IIIA element of the periodic table.
According to an aspect of the invention, the alkali earth metal is one of magnesium (Mg), strontium (Sr), calcium (Ca), and barium (Ba).
According to another aspect of the invention, the element denoted by A is selected from the group consisting of Ce, Pr, Eu, Tb, and Tm is added in an amount of 0.05-5 mol % based on 1 mole of the Ti.
According to yet another aspect of the invention, the Group IIIA element is one of aluminum (Al), gallium (Ga), indium (In), and thallium (TI).
According to still another aspect of the invention, the Group IIIA element is added in an amount of 0.05-80 mol % based on 1 mol of the Ti.
According to yet still another aspect of the invention, the phosphor contains Sm in a range of 0.0001-0.05 mol % based on 1 mol of the Ti.